Mario Mix contains Mario themed songs. And Waka Laka is not in it. There is a story mode which I think is where you unlock songs. Check the DDR game database for the songlist

EDIT: I just noticed you joined yesterday, welcome! I'm guessing you're new to the site so I'll link you to the game database:http://zenius-i-vanisher.com/v5beta/ddrgamedb.php
Just select the game from the list. It's sorted like this VERSION - COUNTRY - RELEASE DATE

Mario Mix is okay... it has 29/30 songs from what I remember, with all of them essentially being remixes of popular Mario songs. There are a handful that are either totally original or remixes of classical songs. And from what I remember, you have to go through the story mode at least twice to get everything unlocked, but I'd also like to mention that the story mode on here is made for like 5-year olds, it's just that easy. The charts have no rated levels, but it goes up to 8's/9's from what most people guess. And I think you have to unlock all the hardest charts by playing the easier charts first. I'd suggest downloading the simfiles for Stepmania first, so you can get a better look at the content before spending any money. If you have a Wii, I suggest getting Hottest Party first if you haven't already.

I had DDR Hottest Party but sold it because I was disapponted with Tokyo Evolution song or whatever it called. It felt like why put a song in there, if its impossible to unlock.

But that's the fun in it!

Once you get it, damn is it ever fun to play...

Quote: GeoStelarSP

I mean when you start off with the game, do you only have like 3-5 songs? or how does it work?

You have no songs, and you have to play through the game on light (easy), which seems like beginner. If you're starting DDR and have never played it, it's a good game, but if you're pro (like me), then don't buy it.